From: Zhao Heming <heming.zhao@suse.com>
Date: Sat, 3 Apr 2021 03:01:25 +0000 (+0800)
Subject: md: md_open returns -EBUSY when entering racing area
X-Git-Tag: v5.4.119~210
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=79c1bfae668d34db9b946a5de86d90a615cca0b1;p=users%2Fdwmw2%2Flinux.git

md: md_open returns -EBUSY when entering racing area

commit 6a4db2a60306eb65bfb14ccc9fde035b74a4b4e7 upstream.

commit d3374825ce57 ("md: make devices disappear when they are no longer
needed.") introduced protection between mddev creating & removing. The
md_open shouldn't create mddev when all_mddevs list doesn't contain
mddev. With currently code logic, there will be very easy to trigger
soft lockup in non-preempt env.

This patch changes md_open returning from -ERESTARTSYS to -EBUSY, which
will break the infinitely retry when md_open enter racing area.

This patch is partly fix soft lockup issue, full fix needs mddev_find
is split into two functions: mddev_find & mddev_find_or_alloc. And
md_open should call new mddev_find (it only does searching job).

For more detail, please refer with Christoph's "split mddev_find" patch
in later commits.
---

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 9abdefd623e49..2f7d29711758d 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7638,8 +7638,7 @@ static int md_open(struct block_device *bdev, fmode_t mode)
 		/* Wait until bdev->bd_disk is definitely gone */
 		if (work_pending(&mddev->del_work))
 			flush_workqueue(md_misc_wq);
-		/* Then retry the open from the top */
-		return -ERESTARTSYS;
+		return -EBUSY;
 	}
 	BUG_ON(mddev != bdev->bd_disk->private_data);